Currently we are working on UG documentation and we will publish it as soon as possible, until then please create an incident for your requirements, we are happy to assist you. Regarding the samples in XAML page, we have create "Multiple Charts” page using XAML designing under ChartSample demo and we will migrate the designing to XAML for all the samples in future. Also we have prepared the simple sample using XAML page for your reference, please find it from the following location,

We would like to let you know that Minimum and Maximum properties are nullable in NumericalAxis, and currently there is a bug in Xamarin to set the nullable properties in XAML, please refer the following Xamarin bugzilla defect report regarding this. Until this issue is fixed please make use of the workaround. We can set those properties as shown in the below code snippet.